The microstructure, grain alignment, superconducting and thermal transport properties of Ni-substituted Bi-2212 rods grown at two different speeds (15 and 30 mm h(-1)) through the Laser Floating Zone method, have been evaluated. Significant variations in grain size, grain alignment, electrical and thermoelectric power properties have been observed for the rods depending on the growth and substitution rates. The highest aligned structure was obtained on unsubstituted rods grown at 15 mm h(-1). Both increased substitution and growth rates degraded the grain alignment. The presence of Ni-based secondary phases showed that Ni is not totally incorporated into the crystal structure, which, in turn, caused a decrease on the average grain size of the rods. With increasing Ni concentration, peak values of thermoelectric power of the rods, which lie between 3.8 and 6.4 mu VK-1, monotonically decreased while thermal conductivity values did not show any systematic change. The activation energy of flux motion, Uo, was calculated from the field dependent resistivity-temperature curves in a range of 0-8 T. Superconducting transition temperatures, T-c(onset) and T-c(offset), and activation energy, U-o, were found to decrease with increasing Ni contents and applied magnetic field. It has been estimated from the magnetic field dependence of activation energy of the samples that plastic creep of the collective vortices is dominant in the rods.
C1 [Ozabaci, M.; Yakinci, M. E.] Inonu Univ, Sci & Technol Res Ctr, TR-44280 Malatya, Turkey.
[Kizilaslan, O.] Inonu Univ, Dept Phys, Fac Arts & Sci, TR-44280 Malatya, Turkey.
[Madre, M. A.; Sotelo, A.] Univ Zaragoza, ICMA CSIC, Zaragoza 50018, Spain.
[Yakinci, M. E.] Inonu Univ, Dept Biomed Engn, Fac Engn, TR-44280 Malatya, Turkey.